Engine emission control systems may utilize various exhaust sensors. One example sensor may be a particulate matter sensor which indicates particulate matter mass and/or concentration in exhaust gas. In one example, the particulate matter sensor may operate by accumulating particulate matter over time and providing an indication of the degree of accumulation as a measure of exhaust particulate matter levels.
Particulate matter sensors may correlate a measured change in electrical conductivity (or resistivity) between a pair of electrodes placed on a substrate surface of the sensor with the amount of particulate matter deposited between the electrodes. Particulate matter sensors may encounter problems with non-uniform deposition of soot on the sensor due to a bias in flow distribution across the surface of the sensor. Further, particulate matter sensors may be prone to contamination from an impingement of water droplets and/or larger particulates present in the exhaust gases. This contamination may lead to errors in sensor output.
Other attempts to address particulate matter sensor performance include guiding a portion of exhaust toward the particulate matter sensor. One example approach is shown by Liu et al. in U.S. Pat. No. 8,756,913. Therein, a pair of intersecting tubes are located along an exhaust passage with a sensor located in an upper portion of the exhaust passage fluidly coupled to an axial tube of the pair of tubes. The tubes are configured to receive exhaust gas from a variety of locations within the exhaust passage to increase an accuracy of data provided by the sensor.
However, the inventors herein have recognized potential issues with such systems. As one example, the pair of tubes may conduct large particulate matter and/or water droplets onto the sensor. This may decrease a reliability of data provided by the sensor with regards to PF degradation.
In one example, the issues described above may be addressed by a method comprising rotating a screen of a particulate matter sensor periodically via an actuator and indicating leakage of a particulate filter based on an amount of power supplied to the actuator. In this way, the amount of power supplied to the actuator increases as particulate matter increases friction experienced by the screen during the periodic rotations.
As one example, the screen is rotated against a filter in the particulate matter sensor each fixed period interval. The screen is rotated a threshold angle, wherein an amount of power supplied to the screen is monitored. The screen is rotated back to its original starting position and the filter is regenerated back to a state comprising less particulate matter stored thereon. By doing this, the filter in the particulate matter sensor may comprise a substantially similar amount of particulate matter following the rotation of the screen. The particulate matter sensor is located downstream of a particulate matter filter located in the exhaust passage. The particulate matter filter undergoes regenerations to enable the particulate matter filter to continue to capture particulate matter. However, the particulate matter filter may degrade following multiple regeneration events experienced over time. The degradation may include one or more of cracks, leaks, and holes. As such, a greater amount of particulate matter may flow to the filter in the particulate matter sensor, thereby increasing an amount of power needed to rotate the screen. If the amount of power exceeds a threshold amount of power, then the particulate matter filter in the exhaust passage may be degraded.
As another example, additionally or alternatively, the particulate matter sensor does not include a screen. However, the particulate matter sensor is configured to regenerate the filter each fixed period interval, as described above. Over time, the particulate matter filter in the exhaust passage becomes degraded. This may result in higher regeneration temperatures experienced by the filter in the particulate matter sensor. As such, the particulate matter filter in the exhaust passage may be degraded when a regeneration temperature of the filter in the particulate matter sensor is greater than a threshold temperature.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
FIGS. 2-3 and 6 are shown approximately to scale.